Sakuya's knife lines (her EX attacks) in PoFV. The hitboxes on those things seem larger than they should be (especially compared to the knives that come from her spells and boss summon), and I've often gotten hit by them when I thought for sure that they didn't touch my hitbox.
Also, the rice bullets after they shrink during Final Boss Kanako's second spell card in MoF (Rice Porridge in Tube "God's Rice Porridge", Forgotten Husk "Unremembered Crop", Divine Husk "Divining Crop"). Nearly as unfriendly as Sakuya's knife lines above.
And, of course, all bullets during Final Boss Sukuna's fourth spell card in DDC (Mallet "You Grow Bigger!") when not using Reimu, because it feels to me like Marisa's and Sakuya's hitboxes are actually larger than the enlarged hitbox dot shows, and I get hit whenever a bullet gets remotely close to what appears to be my hitbox.